Trace gas and particle measurements taken during the CRYSTAL-FACE mission are used to examine mixing in the summer subtropical lower stratosphere. Vigorous convection in the central and eastern United States injected a significant amount of tropospheric air into the lower stratosphere, which was subsequently advected over the region sampled during the CRYSTAL-FACE mission. Aerosols produced by biomass burning were observed over Florida during a time period with a large number of forest fires in the western United States and eastern Canada, providing evidence of convective injection of tropospheric air into the lower stratosphere. The circumstances of the large-scale flow pattern in the upper troposphere and lower stratosphere, vigorous summertime convection, abundant forest fires, and the downstream sampling allow a unique view of mixing in the lower stratosphere. We calculate the fractions of midlatitude tropospheric air in the sampled lower stratosphere and mixing rates on the basis of consistency between a number of tracer-tracer correlations. The tropospheric endpoints to the mixing estimates give an indication of midlatitude continental convective input into the lower stratosphere. We also discuss the possible impact of summertime midlatitude convection on the composition of the stratosphere as a whole.